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Levers

Levers. What is a Lever?!. A lever is a rigid bar that rotates around an axis (fulcrum). In Our Body. Bones  act as the rigid bar Joints  act as the axis (fulcrum) Muscle  apply the force. A Lever Consists of Three Components.

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Levers

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  1. Levers

  2. What is a Lever?! • A lever is a rigid bar that rotates around an axis (fulcrum). In Our Body • Bones  act as the rigid bar • Joints  act as the axis (fulcrum) • Muscle  apply the force

  3. A Lever Consists of Three Components • Resistance Force Arm: the perpendicular distance from the line of action of the resistance to the fulcrum. • Effort Force Arm: the perpendicular distance from the line of action of the effort force to the fulcrum. • Fulcrum: the axis which a lever may rotate around

  4. Classes of Levers • First Class Lever • Second Class Lever • Third Class Lever

  5. First Class Lever • The fulcrum is between the effort force & the resistance force. • The effort force & the resistance can be at an equal distance from the fulcrum, or one may be farther away than the other Mechanical Examples • Scissor • teeter-totter

  6. Anatomical Example Extension of the head • Fulcrum: Atlanto-occipital joint • Resistance: weight of the head • Effort force: neck extensors

  7. Second Class Lever • The resistance is between the effort force & the fulcrum. • The effort force & the resistance are on the same side of the axis, with the resistance closer to the fulcrum Mechanical Examples • Wheel-barrow • Nutcracker

  8. Anatomical Example Rising of heals to stand on toes • Fulcrum: metatarsophalangeal joints • Resistance: weight of the body • Effort force: Planterflexors (Calf muscles)

  9. Third Class Lever • The effort force is between the resistance & the fulcrum. • The effort force acts between the fulcrum & the line of resistance force Mechanical Examples • Fishing poles Shoveling • Tweezers

  10. Anatomical Example Forearm Flexion • Fulcrum: Elbow joint • Resistance: object held in hand • Effort force: biceps muscle

  11. What is Mechanical Advantage?! • Mechanical advantage is the ratio of force arm to resistance arm of a giver lever. • MA = effort force arm / resistance force arm

  12. What If Mechanical Advantage = 1 • Effort force arm = resistance force arm • There will be a change in the direction of movement only

  13. What If Mechanical Advantage > 1 • Effort force is smaller than resistance force •  distance effort force moves, meaning that the distance moved by the effort is greater than the distance moved by the resistance

  14. What If Mechanical Advantage < 1 • Effort force in more than resistance force •  distance effort force moves, meaning that the distance moved by the effort is lesser than the distance moved by the resistance

  15. In First Class Lever Mechanical advantage can be: • = 1 • < 1 • > 1 • Can be used to gain force advantage or distance/speed advantage

  16. In Second Class Lever • Mechanical advantage can be is ALWAYS > 1 • Used to gain force advantage In Third Class Lever • Mechanical advantage can be is ALWAYS < 1 • Most human levers are class III

  17.  Study Hard & Good Luck 

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